Unravelling the Significance of Phosphoenolpyruvate Carboxylase in Phosphate Starvation Responses.

Low phosphate availability is a major concern for agriculture. Plants develop a plethora of responses to improve phosphate acquisition, known as phosphate starvation responses (PSR). Among them, the induction of phosphoenolpyruvate carboxylase (PEPC) has been described in many plants. However, most studies have been conducted in the absence of phosphate, thus the real impact of PEPC in PSR is missing as there is no phosphate to take up. In this study, we used modified sorghum plants silenced in the main PEPC isozyme in roots, SbPPC3, and analyzed the role of PEPC in the presence of insoluble calcium phosphate (PCa), showing a phosphate starvation phenotype in silenced but not in WT plants. Interestingly, root exudation of citrate was not reduced in silenced plants, probably due to a higher citrate synthase activity, but it was reduced for succinate, another compound with phosphate solubilisation capacity. Finally, silenced plants accumulated less P in roots with PCa, leading to a reduced phosphate acquisition efficiency (PAE). Our results show, for the first time, the actual role of PEPC in phosphate solubilisation through succinate exudation, proposing PPC3 as a specific target to improve PAE in plants.